Composite rotor for flywheel energy storage system

ABSTRACT

Composite rotors provided herein include a rotor body extending along a longitudinal axis including a first component extending longitudinally along at least a portion of the rotor body and a second component extending longitudinally along at least a portion of the rotor body, at least a portion of the second component disposed concentrically around the first component, wherein the first component and the second component together define an internal region, wherein a radial thickness of the first component and a radial thickness of the second component vary along the longitudinal axis. The composite rotor also includes at least one magnet disposed on an inner surface of at least one of the first component or the second component within the internal region.

FIELD OF THE INVENTION

This invention relates to flywheel rotors and more particularly tocomposite rotors for flywheels.

BACKGROUND OF THE INVENTION

Flywheels have conventionally been used in connection with applicationsrequiring stored energy. Many such applications are in the electricalpower industry, particularly where short duration, high power output isrequired over many cycles throughout years of continuous operation. Moregenerally, flywheels are useful where power fluctuations need to bemanaged or energy needs to be stored. Flywheel applications typicallyfall into three classifications: 1) power management, 2) energybalancing, and 3) persistent energy storage applications. Theseclassifications can cover a broad array of applications, including, forexample, rapid transit power management, mining, industry, renewablesintegration, grid frequency regulation, pulsed power, electromagneticaircraft launch, rotary UPS (uninterrupted power supply), and materialhandling. The storage duration (cycle time) and cyclic life requirementsof each application can vary widely.

For some applications, flywheels can replace batteries (e.g., lithiumion) and capacitors/ultra-caps for more efficient energy storage andpower management. For example, for high-cycle and/or long-term storageapplications, batteries generally cannot meet life and performancerequirements. Additionally, capacitors, even if requirements can be met,are generally more expensive than flywheels for similar or lesserperformance.

However, because of conventionally performance-stealing,cost-prohibitive challenges associated with increasing scale, there is alarge, mostly untapped market for flywheels in power managementapplications requiring high cyclic content and rapid transient responsetimes (e.g., rapid transit or grid integration for wind and solar). Forsuch high-power, rapid-cycle flywheel applications (e.g., wherein powerinputs and outputs of 1 MW to 10 MW are required to be rapidly cycledover a transient response time between 10 seconds to five (5) minutes),a large drive-motor/generator is required. Such motor/generators requiremore complex magnet arrays and power control systems to manage increasedsize, speed, and power as well as more complex and robust mechanical andcooling systems to withstand the increased stresses and dissipated heatassociated with the increased size, speed, and power. Furthermore, wearand tear associated with such rapid cycling can substantially limitcyclic life and increase maintenance requirements for the flywheel, thusdriving high replacement costs and resulting in significant maintenancedowntime.

SUMMARY OF INVENTION

It is an object of the invention to provide a continuously operable,high cycle-life flywheel system scalable for high power, rapid cycleapplications.

In one aspect, a composite rotor is provided. The composite rotorincludes a rotor body extending along a longitudinal axis. The rotorbody includes a first component extending longitudinally along at leasta portion of the rotor body. The rotor body also includes a secondcomponent extending longitudinally along at least a portion of the rotorbody, at least a portion of the second component disposed concentricallyaround the first component. The rotor body also includes wherein thefirst component and the second component together define an internalregion. The rotor body also includes wherein a radial thickness of thefirst component and a radial thickness of the second component varyalong the longitudinal axis. The composite rotor also includes at leastone magnet disposed on an inner surface of at least one of the firstcomponent or the second component within the internal region.

In some embodiments, the first component is constructed of a firstfiber-reinforced composite. In some embodiments, the second component isconstructed of a second fiber-reinforced composite. In some embodiments,the first fiber-reinforced composite of the first component is overwoundwith the second fiber-reinforced composite of the second component toform the composite rotor. In some embodiments, the first and secondfiber-reinforced composites are each constructed from at least one of aglass fiber, an aramid fiber, a carbon fiber, a quartz fiber, a boronfiber, a ceramic fiber, a natural fiber, or combinations thereof. Insome embodiments, a resin matrix of each of the first and secondfiber-reinforced composites is constructed from at least one of apolyester resin, a vinylester resin, an epoxy resin, a phenolic, acyanate ester, a silicone, a polyurethane, a bismaleimide, a polyimide,or combinations thereof.

In some embodiments, the first fiber-reinforced composite includes aglass reinforcing fiber. In some embodiments, the secondfiber-reinforced composite includes a carbon reinforcing fiber. In someembodiments, a same resin matrix is used in both of the first and secondfiber-reinforced composites. In some embodiments, a resin matrix of thefirst fiber-reinforced composite is different than a resin matrix of thesecond fiber-reinforced composite.

In some embodiments, the second component further comprises an internalrecess. In some embodiments, the first component is disposed in theinternal recess. In some embodiments, the inner surface on which the atleast one magnet is disposed is an inner surface of the secondcomponent, the inner surface being longitudinally spaced apart from theinternal recess of the second component in which the first component isdisposed. In some embodiments, an inner bearing surface of the firstcomponent is operatively engaged with a rotor hub. In some embodiments,the rotor body and at least one magnet form a composite rotor of aflywheel energy storage system. In some embodiments, the rotor bodyincludes a third component extending longitudinally along a portion ofthe rotor body longitudinally spaced apart from the first component, atleast a second portion of the second component disposed concentricallyaround the third component. In some embodiments, a radial thickness ofthe third component varies along the longitudinal axis. In someembodiments, the third component is constructed of at least one of thefirst fiber-reinforced composite or a third fiber-reinforced composite.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the present disclosure will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1 is a cross-sectional view of a flywheel energy storage system inaccordance with various embodiments.

FIG. 2A is a perspective view of a flywheel stator assembly inaccordance with various embodiments.

FIG. 2B is a perspective view of a single stator pole in accordance withvarious embodiments.

FIG. 3 is an exploded view of a plurality of composite lamination layersused to construct the flywheel stator assembly in accordance withvarious embodiments.

FIG. 4 is a cross-sectional view of the flywheel stator assemblyillustrating a coolant flowpath formed therein in accordance withvarious embodiments.

FIG. 5 is a cross-sectional detail view of an inlet plenum of a statorpole in accordance with various embodiments.

FIG. 6A is a detail cross-sectional side view of a stator-plenum chamberassembly in accordance with various embodiments.

FIG. 6B is a detail top view of the stator assembly in accordance withvarious embodiments.

FIG. 7A is a circumferential map of a motor magnet array in accordancewith various embodiments.

FIG. 7B is a cross-sectional view of the motor magnet array of FIG. 7Aapplied to an inner surface of a flywheel rotor in accordance withvarious embodiments

FIG. 8 is a perspective view of a flywheel rotor hub in accordance withvarious embodiments.

FIG. 9 is a cross-sectional view of a flywheel bearing-rotor shaftassembly in accordance with various embodiments.

FIG. 10 is a perspective view of a flywheel rotor shaft in accordancewith various embodiments.

FIG. 11A is a perspective view of a flywheel bearing housing inaccordance with various embodiments.

FIG. 11B is a top view of the flywheel bearing housing of FIG. 5A inaccordance with various embodiments.

FIGS. 12A, 12B, and 12C are top perspective, bottom perspective, andcross-sectional top perspective views of a flywheel baseplate inaccordance with various embodiments.

FIG. 13 is a cross-sectional view of a flywheel housing assembly inaccordance with various embodiments.

FIG. 14 is a cross-sectional view of a flywheel assembly having acontainment liner in accordance with various embodiments.

FIG. 15 is a system diagram of a flywheel system for use in connectionwith a rapid transit rail system.

FIG. 16 is an electrical schematic of a flywheel power electronicssystem in accordance with various embodiments.

DETAILED DESCRIPTION OF THE INVENTION

The disclosure and the various features and advantageous details thereofare explained more fully with reference to the non-limiting embodimentsand examples that are described and/or illustrated in the accompanyingdrawings and detailed in the following description. It should be notedthat the features illustrated in the drawings are not necessarily drawnto scale, and features of one embodiment may be employed with otherembodiments, as the skilled artisan would recognize, even if notexplicitly stated herein.

Descriptions of well-known components and processing techniques may beomitted to not unnecessarily obscure the embodiments of the disclosure.The examples used herein are intended merely to facilitate anunderstanding of ways in which the disclosure may be practiced and tofurther enable those of skill in the art to practice the embodiments ofthe disclosure. Accordingly, the examples and embodiments herein shouldnot be construed as limiting the scope of the disclosure. Moreover, itis noted that like reference numerals represent similar parts throughoutthe several views of the drawings.

Provided herein are continuously operable, high cycle-life flywheelsystems scalable for high power, rapid cycle applications. Moreparticularly, referring now to FIG. 1, in some embodiments, an“inside-out” flywheel assembly 100 (hereinafter “flywheel”) is providedwherein a stator assembly 200 is positioned internal to a compositerotor 300 for rotation about the stator assembly 200. Cooling can beprovided via internally cooled stator poles 203 of the stator assembly200, the stator poles 203 configured to redirect coolant into fluidcontact with windings 207 of the stator assembly 200. Concentricity ofthe rotor 300 can be regulated by a circumferentially expandable rotorhub 350 for maintaining operative engagement between the composite rotor300 and a rotor shaft assembly 400 extending along a longitudinal axisof the flywheel 100. Generally, the shaft assembly 400 can be positionedwithin a bearing housing 450 within the stator assembly 200. The entireflywheel assembly 100, in some embodiments, can generally be enclosed bya housing flywheel 600 mounted between a baseplate 500 and a lid 650. Insome embodiments, a floating containment liner 700 can be provided aboutthe rotor 300 to retain the rotor 300 in the event of mechanicalfailure.

Stator Assembly

Referring now to FIGS. 2A, 2B, 3, and 4, stator assembly 200 includes aninner body 201 extending along a longitudinal axis between a first endand a second end, an outer body 203 extending around and along the innerbody 201, and a plurality of stator poles 205 extending radiallytherebetween. Each of the stator poles 205 includes one or more windings207 extending therearound.

In some embodiments, the inner body 201 and stator poles 205 can beintegrally formed as shown, for example in FIG. 3. In such embodiments,the stator assembly 200 can, for example, include the circular innerbody 201 having a plurality (e.g., 21 as shown) of integral stator poles205 extending therefrom. Each stator pole 205, as shown in FIGS. 2B and3, can include a tooth 205 a and a slot 205 b. As shown in FIGS. 2A and4, the windings 207 can generally be wrapped about the tooth 205 a andthe slot 205 b can both add structural stiffness to the stator pole 205and operate to retain the windings 207 thereon.

Referring again to FIG. 3, in some embodiments, in order to facilitatethe formation of variant internal structures (e.g., inlet 209, inletplenum 211, internal passages 213, outlet plenum 215, and outlet 217described below) and to reduce eddy currents within the stator assembly200, the integrated inner body 201 and stator poles 205 can be formed bya stacked lamination of a plurality of stator layers 206. For example,in some embodiments, the stacked lamination can be made up of 1160stator layers 206, each lamination being 0.025″ thick and defining aportion of the inner body 201 and 21 integrated stator poles 205.However, it will be apparent in view of this disclosure that stackedlaminations, in accordance with various embodiments, can include anynumber of integrated stator poles 205 and any suitable number of statorlayers 206, each layer having any suitable thickness. Each stator layer206 can be constructed of any suitable material for use in connectionwith a stator of an electrical motor/generator such as, for example, AKelectrical steel, any cold-rolled ferromagnetic steel, any otherferromagnetic material capable of being formed into a plurality ofstacked laminations, or combinations thereof.

In some embodiments, as shown in FIGS. 2A and 4, the stacked laminationof the stator assembly 200 can be secured by way of an inner ringbracket pair 202 overlaying the inner body 201 at the first and secondends of the stator assembly 200 and by an outer ring bracket pair 204overlaying the slot 205 b at the first and second ends of the statorassembly 200. Each of the inner and out ring bracket pairs can beconnected (e.g., by tie bolts 208 as shown) to compress and secure thestacked lamination to form the inner body 201 and the stator poles 205.

The windings 207 can generally be wound about the tooth 205 a of eachstator pole 205. The windings 207 can be formed from any suitablewinding wire, including, for example, Litz type 8 wire. As shown inFIGS. 2A and 4, the stator assembly 200 can include three (3) turns of a14 Litz wire bundle around each stator pole 205 tooth 205 a, thusproviding 42 Litz wires wrapped around each stator pole 205. However, itwill be apparent in view of this disclosure that, in accordance withvarious embodiments, bundles having any number of Litz wires can beturned around each stator pole 205 tooth 205 a any number of times.

As best shown in FIGS. 2B and 14, the outer body 203 can generallyextend around the slots 205 b and outer ring bracket pair 204 forforming an outer diameter of the stator assembly 200. As shown, theouter body 203 is a separate element from the inner body 201 and statorpoles formed by the stacked lamination. However, it will be apparent inview of this disclosure that, in accordance with various embodiments,the outer body can be integrally formed with the stacked laminationand/or the outer ring bracket pair 204 or can otherwise be bondedthereto (e.g., by welding, adhesive bonding, brazing, or any othersuitable means).

As shown and described herein, the stacked lamination and outer body areconstructed to form a stator assembly 200 of about 30″ in length, anouter diameter of about 20″, and an inner diameter of about 13″.However, it will be apparent in view of this disclosure that the statorassembly 200 can be constructed to have any length, outer diameter,and/or inner diameter according to electrical, mechanical, and/orthermal requirements of each particular flywheel 100. For example, theouter diameter can generally be matched to an inner diameter of a motormagnet array 309 of the rotor 300 to achieve a prescribed gaptherebetween at the stator 200-rotor 300 interface.

Stator Cooling

As noted herein above, large scale electric motor/generators producesignificant excess thermal energy (heat), which must be dissipatedduring operation. However, direct cooling of the rotor 300-stator 200interface is impossible because electric motor/generators generallyrequire such interface to be maintained at vacuum pressure. Also, due tothe high rotational speed of the rotor 300, direct cooling of the rotoris generally impractical. Smaller conventional flywheel systemssometimes provide cooling of a cylindrical core of a stator assembly toserve as a heat sink for the stator poles. However, such systems are notscalable because larger stator poles and higher power inputs and outputsgenerate substantially more heat, thus rendering core heat sinksprogressively less effective.

As provided herein, such cooling challenges are overcome by amulti-function cooling of the stator assembly 200. In particular,referring now to FIGS. 4, 6A, and 6B, the stator assembly 200 providesfor scalable cooling of the flywheel 100 sufficient for cooling large,high power systems. Generally, the stator assembly 200 facilitates bothinternal cooling of the stator poles 205 and direct fluid contactcooling of the windings 207 by flowing coolant up through the statorpoles 205 and then redirecting that flow down over the windings 207between the inner body 201 and the outer body 203.

As shown in FIGS. 3 and 4, coolant flows into each stator pole 205 at afirst end of the stator assembly 200 via an inlet 209 formed in theinner body 201 proximate a root of each respective stator pole 205. Asbest shown in FIG. 5, coolant can then flow from the inlet 209 into aninlet plenum 211 for distribution along a radial length of the statorpole 205 to permit subsequent flow into one or more of a plurality ofinternal passages 213. Referring again to FIG. 4 internal passages 213generally extend within each stator pole 205 along a longitudinal lengththereof to provide internal cooling of the stator poles 205. Coolantexiting the internal passages 213 can flow into an outlet plenum 215 andthen exit the stator pole 205 via an outlet 217 formed in the inner body201 at the second end of the stator assembly 200.

As best shown in FIGS. 6A and 6B, coolant exiting the outlet 217 canthen enter a plenum chamber 219 configured to redirect the flow backtoward the first end of the stator assembly 200 and into fluid contactwith the windings 207 between the inner body 201 and the outer body 203.The plenum chamber 219 can generally be defined between the outer body203, a plenum cap 220, and a bearing containment column 453 of thebearing housing 450

In some embodiments, a spray bar 222 or other diffuser can be radiallyinterposed in the plenum chamber 219 between the outlet 217 and thewindings 207 to distribute the coolant flowing into fluid contact withthe windings 207. Despite the coolant flowing into direct fluid contactwith the windings 207 external to the stator poles 205, the pumpedvacuum at the stator 200-rotor 300 interface is maintained because, asdescribed above, the outer body 203 is, as best shown in FIG. 6A, sealedagainst a plenum flange 221 of the plenum chamber 219 at the second endof the stator assembly 200 and, as best shown in FIG. 14, sealed againstthe sealing flange 455 of the bearing housing 450 at the first end.Thus, no coolant can flow or leak into the stator 200-rotor 300interface.

The described stator cooling configuration advantageously providesenhanced heat dissipation as compared to conventional cooled innercores. Initially, conventional cooled inner cores are inherently spacedapart from the stator-rotor interface by the radial length of any statorpoles. Therefore, the larger the scale, the larger the stator poles andthe less effective the cooling. By contrast, the cooled stator poles 205of the stator assembly 200 described herein provide a more robust heatsink closer to the vacuum pumped stator 200-rotor 300 interface.Furthermore, the direct fluid contact cooling of both the windings 207and, incidentally, the outer body 203, provides additional cooling ofthe motor/generator components and the stator 200-rotor 300 interfaceduring operation of the flywheel 100.

Composite Rotor

Referring again to FIG. 1, a composite rotor 300 generally provides theenergy storage for the flywheel 100. In particular the flywheel 100,when storing energy, acts as an electric motor to spin the flywheel 100at high RPM, thereby converting the input electric energy intorotational kinetic energy stored in the rotor 300. Then, when theflywheel 100 needs to output the stored energy, the flywheel 100reverses polarity to act as an electrical generator, thereby convertingthe stored kinetic energy back into electrical energy for delivery to asystem having an electrical demand.

The composite rotor 300 can include a rotor body 301 extending along thelongitudinal axis of the flywheel 100 and around the stator assembly200. The rotor body 301 includes a first component 303 constructed of afirst material and extending along at least a portion of the rotor body301 and a second component 305 constructed of a second material andextending longitudinally along at least a portion of the rotor body 301such that at least a portion of the second component 305 is disposedconcentrically around the first component 303.

In some embodiments, the rotor body 301 can further include a thirdcomponent 306 longitudinally spaced apart from the first component andalso having a portion of the second component 305 disposedconcentrically therearound. For example, as shown in FIG. 1, the thirdcomponent 306 can be positioned at the base of the rotor body 301proximate the bearing housing 450. In some embodiments, as shown, forexample, in FIG. 1, at least a portion of the third component can extendconcentrically around the sealing flange 455 of the bearing housing 455.

In combination, the first component 303 and the second component 305,and any additional components such as the third component 306, form therotor body 301. The rotor body 301 can generally include an internalregion 307 defined by an inner diameter of the rotor body 301. Ingeneral, the rotor body 301 can preferably extend along the longitudinalaxis at least partially coincident with the stator assembly 200. Forexample, as shown in FIG. 1, the stator assembly 200 can be positionedentirely within the internal region 307 of the rotor body 301. Thispositioning advantageously permits the stator poles 205 and windings 207to interact with one or more motor magnets 311 of a magnet array 309(e.g., a Halbach cylinder) disposed along the inner diameter of therotor body 301 (see FIGS. 7A and 7B).

The inner diameter of the rotor body 301 can generally be sized suchthat a prescribed gap is maintained between an inner diameter of themagnet array 309 and the outer diameter of the stator array 200 at thestator 200-rotor 300 interface. An outer diameter of the rotor body cangenerally be configured to provide sufficient thickness to withstandoperational conditions (e.g., high speed rotation) and furtherconfigured, in combination with rotor body 301 length, to provide arotor body 301 of sufficient mass to store the desired quantity ofenergy. For example, in the embodiment shown in FIG. 1, the overallrotor body 301 is about five (5) feet long and includes an outerdiameter of about three (3) feet and an inner diameter of about two (2)feet.

As shown in FIG. 1, although an overall thickness of the rotor body isgenerally consistent, the radial thicknesses of the first component 303and the second component 305 vary along the longitudinal axis. Forexample, as shown in FIG. 1, the second component 305 defines aninternal recess with the first component 303 disposed therein. Suchvariation, in some embodiments, can be driven by differing loadconditions along the length of the rotor body 301. In that regard,generally, radial growth of the rotor body 301 under rotational load,both at the inner and outer diameters, should be uniform duringoperation of the flywheel. Otherwise, at full rotational speed, therotor 300 will be imbalanced, limiting flywheel 100 performance andpotentially causing mechanical failure. However, different portions ofthe rotor body 301 experience different levels of stress duringoperation of the flywheel 100. For example, the motor magnets 311 of themagnet array 309 are disposed along at least a portion of the rotor body301 and create a “dead load” (i.e. not a self-supporting load) in thatarea, which the rotor body 301 needs to support. Similarly, otherportions of the rotor body 301 may bear against and be at leastpartially supported by a rotor hub 350. Thus, for example, the hoopstiffness may need to be greater in some locations than in others.Accordingly, the varying thicknesses of the first component 303 and thesecond component 305 can, in some embodiments, be configured towithstand variant loads while providing uniform radial growth of therotor body 301 during operation of the flywheel 100.

In addition, such a multi-component, varying thickness construction isimpossible in conventional multi-component rotors. In particular,conventional multi-component rotors require a press fit between thecomponents, which necessarily dictates only cylindrical components ofconstant thickness. Furthermore, in such configurations, the press fitis prone to loosening over time as the rotor material relaxes. As thepress fit loosens, the components can rotate at different speeds,potentially causing loss of flywheel performance and/or mechanicalfailure.

The rotor body 301 of the composite rotor 300 described herein is ableto achieve such a configuration because the first component 303 isconstructed of a first fiber-reinforced composite and the secondcomponent 305 is constructed of a second fiber-reinforced composite.More particularly, the rotor body 301 is constructed by overwinding thefirst fiber-reinforced composite of the first component 303 with thesecond fiber-reinforced composite of the second component 305 asappropriate to match a desired thickness variation profile.

In some embodiments, where, for example, the fiber-reinforced compositeof the first component 303 and the fiber-reinforced composite of thesecond component 305 require different resin matrixes, the overwindingcan be executed by first applying the resin matrix of the firstcomponent 303 to wet and/or cure the reinforcing fibers of the firstcomponent 303, overwinding the first component 303 with the reinforcingfibers of the second component 305, and then applying the resin matrixof the second component 305. Alternatively, in some embodiments, where,for example, a common resin matrix can be used for the fiber-reinforcedcomposites of both the first component 303 and the second component 305,the dry reinforcing fibers of the first component 303 can be overwoundwith the dry reinforcing fibers of the second component 305. The commonresin matrix can then be applied to the dry reinforcing fibers of bothcomponents 303, 305 together.

Thus, because the first component 303 is overwound by the secondcomponent 305, the components are permanently bonded and will neverseparate. Furthermore, because the first component 303 is overwound bythe second component 305, thereby obviating any need to press the firstcomponent 303 into the second component 305, each component can exhibitvarying thicknesses along the length of the rotor body 301.

The fiber-reinforced composites of the first component 303 and thesecond component 305 can be any suitable composite. For example, thereinforcing fibers of the first and second fiber-reinforced compositescan include at least one of a glass fiber, an aramid fiber, a carbonfiber, a quartz fiber, a boron fiber, a ceramic fiber, a natural fiber,any other suitable fiber, or combinations thereof. Also for example, theresin matrix of each of the first and second fiber-reinforced compositescan include at least one of a polyester resin, a vinylester resin, anepoxy resin, a phenolic, a cyanate ester, a silicone, a polyurethane, abismaleimide, a polyimide, any other suitable resin matrix, orcombinations thereof.

In some embodiments, the reinforcing fiber of the first fiber-reinforcedcomposite can include a glass reinforcing fiber and the reinforcingfiber of the second fiber-reinforced composite can include a carbonreinforcing fiber. In some embodiments, for example, the secondcomponent 303 can be made of wound T700 composite material with a+/−89-degree fiber weave and a binder of PPG resin and the firstcomponent 303 can be made of fiberglass.

Motor Magnets

As noted above and shown in FIGS. 7A and 7B, a magnet array 309comprising a plurality of magnets 311 is generally disposed about theinner diameter of the rotor body 301 along at least a portion of thelength of the rotor body 301. The magnets 311 of the magnet array 309generally provide, in combination with the stator poles 205 and windings207, an electromagnetic source for the motor/generator of the flywheel.As described herein, the magnets 311 are permanent magnets. The magnets311 of the magnet array 309 can generally be any suitable permanentmagnet, including, for example, neodymium-iron-boron (NdFeB) magnets. Insome embodiments, for example, the magnets 311 disposed on the innerdiameter of the rotor body 301 can include epoxy bonded NdFeB magnets.

The magnets 311 of the magnet array 309 can generally be arranged in anynumber and manner suitable for producing magnetic flux sufficient tointeract with the stator poles 205 and windings 207. As shown in FIGS.7A and 7B, for example, the magnet array 309 includes 128 magnets 311arrayed and skewed in a Halbach cylinder. As shown, the magnets 311 arebonded to the inner diameter of the composite rotor 300 at roughly a 24″diameter and over roughly 30″ axial length. However, it will be apparentin view of this disclosure that the magnet array 309 can include anyarrangement of any number of magnets 311 bonded over any length of anysized inner rotor diameter in accordance with various embodiments.

Rotor Hub

Referring now to FIG. 8, the rotor hub 350 is configured to provide alinkage between the composite rotor 300 and a rotor shaft 400, therebyproviding overall system centrality for balance stability. In order toprovide such overall system centrality, the rotor hub 350 is required tomaintain contact with the inner diameter of the rotor body 301 at alltimes during operation. However, conventional rotor hubs can experienceuneven radial growth at high rotational speeds, thus potentially losingcontact with portions of the inner diameter of the rotor body 301 and/orlosing balance stability.

The rotor hub 350 described herein includes a frustoconical body 351extending along a longitudinal axis between a base 353 and a frustum355. The frustum 355 is generally configured to interconnect at an innerdiameter thereof with the rotor shaft 401. In some embodiments, aplurality of elongated protrusions 357 or “fingers”, spaced about thecircumference of the base 353 can extend from the base 353 parallel tothe longitudinal axis and toward the frustum 355. In some embodiments,contact pads 359 are formed at a terminal end of each of the elongatedprotrusions 357 for contacting the inner diameter of the rotor body 301.Under rotation, the elongated protrusions 357 of the rotor hub 350 areconfigured to load and flex radially outward to maintain 360 degreecontact between the contact pads 359 and the inner diameter of the rotorbody 301 such that concentricity can be maintained between the rotor hub350 and the rotor 300.

The rotor hub 350, including the frustoconical body 351, the elongatedprotrusions 357, and the contact pads 359, can generally be constructedas a single piece rotor hub 350. In general, the rotor hub 350 can beconstructed from any suitable material, including, for example,composites and/or metals such as steel, aluminum, or alloys, orcombinations thereof. In some embodiments, the rotor hub 350 can beconstructed from a sufficiently flexible material to permit the fingersto grow radially during operation. For example, in some embodiments, therotor hub 350 can be constructed of 7075 aluminum.

In accordance with various embodiments, the frustoconical body 351 caninclude a 50-degree cone angle to provide an enhanced outward radialload at speed. However, it will be apparent in view of this disclosurethat any cone angle can be used in connection with the frustoconicalbody 351 in accordance with various embodiments.

As shown in FIG. 8, the rotor hub 350 can include 24 elongatedprotrusions 357. However, it will be apparent in view of this disclosurethat the rotor hub 350 can include any number of elongated protrusions357 in accordance with various embodiments. In particular, for theembodiment shown in FIG. 8, in some embodiments, each of the elongatedprotrusions 357 can be about six (6) inches long, about 0.5 inchesthick, and about 1.2 inches wide. Furthermore, for the embodiment shownin FIG. 8, in some embodiments, each of the contact pads 359 can beabout 1.5 inches long, about 1.1 inches thick, and about 1.2 incheswide. However, it will be apparent in view of this disclosure that, inaccordance with various embodiments, as dictated by the size andconfiguration of the flywheel 100, the elongated protrusions 357 andcontact pads 359 can be any suitable combination of lengths,thicknesses, and widths.

Shaft Assembly and Bearings

Referring now to FIGS. 9 and 10, a shaft assembly 400 is providedincluding a rotor shaft 401 extending along the longitudinal axis of theflywheel 100 for providing a center of rotation of the rotor 300. Thatis, the shaft assembly 400, particularly the rotor shaft 401, does notcarry any stress load other than its own free hoop during rotation andinstead provides only a center of rotation for the rotor 300 viainterconnection with the rotor hub 350.

The shaft 401, in some embodiments, can be any suitable length (e.g.,about 45″ long) and can have any suitable diameter or range of diametersalong a longitudinal length thereof. For example, the shaft may bebetween about 1″ to about 12″ in diameter. For example, in someembodiments, the shaft 401 may have a core shaft diameter of about 4″expandable to a flange 403 having a diameter of about 10″. In accordancewith various embodiments, the shaft can be constructed of any suitablematerial, including, for example, composites, metals such as low carbonalloy steels (e.g. 4130 or 4340), any other suitable material, orcombinations thereof. In some embodiments, the shaft 401 can be hollow,wherein an inner diameter of the shaft 401 is sized for tuning the rotordynamics translation and 1^(st) bending mode natural frequencies of theshaft 401. For example, a 4″ diameter hollow shaft can include an innerdiameter of about 2.75″.

As shown in FIGS. 1 and 9, the shaft 401 rotates on two magnetic radialbearings 407, a backup mechanical radial bearing 409, and a thrustbearing 411. The two magnetic radial bearings 407, in cooperation withthe shaft 401, define the system centerline. Additionally, the flywheel100, as shown in FIG. 1, includes an upper radial bearing 415 rotatableabout a flywheel barrel 430 extending between the shaft 401 and a lid650 of the flywheel 100 proximate the second end of the flywheel 100.The upper radial bearing 415 provides additional structural support andcentering of the rotor 300 at the second end of the flywheel 100 toprevent tilt or other imbalancing of the rotor 300.

In order to provide improved shaft 401/bearing 407 wear life, there arebearing sleeves 405 disposed about the shaft 401 where each of themagnetic radial bearings 407 and a backup, mechanical bearing 409interface with the shaft. The sleeves 405 can be made of any suitablematerial, including, for example, any metal such as 321 stainless steelor any other suitable for increasing bearing wear life of the shaft 401.Additionally, the flywheel 100 can create substantial axial thrust(up/down) loads during operations. Such axial thrust is generallyreacted out by interaction of a thrust bearing 411 acting on the flange403. In order to measure operational conditions of the flywheel 100, insome embodiments, the shaft assembly 400 can also include one or moresensors. For example, as shown in FIG. 9 the shaft assembly can includea shaft position encoder 413 and/or a radial position sensor 415 fordetecting longitudinal and radial position of the shaft 401.

Referring now to FIGS. 11a and 11B, the bearing housing 450 includes abase 451 mountable to a baseplate 500 of the flywheel 100 and providinginterface passages corresponding to any service ports in the baseplate500. The bearing housing 450 also includes a bearing containment column453 extending upward therefrom. The containment column 453 provides anouter diameter interface for the magnetic bearings 407, 411. The bearingcontainment column 453 can be substantially cylindrical and sized to beinterposed between the shaft assembly 400 and the stator assembly 200for containing the bearings 407, 411 and the shaft 401 during operation.Similarly, the bearing containment column can be any suitable length forcontaining the bearings 407, 411 and shaft 401. For example, in someembodiments, bearing containment column 453 can be about 40″ long andabout one foot in diameter over the length providing bearing interface.

The bearing housing 450 can also serve as an interface for the statorpoles 205/windings 207 as well as a pass-through for cooling services tothe stator assembly 200. In particular, the bearing housing 450 includesa sealing flange 455 extending upward therefrom for sealing against theouter body 203 of the stator assembly 200 to permit maintenance of thepumped vacuum at the stator 200-rotor 300 interface and prevent coolantleakage. The bearing housing 450 also includes supply passages 457extending through the base 451 to permit coolant to pass from a supplyport 501 of the baseplate 500 into the inlets 209 of the stator assembly200 and drain passages 459 extending through the base 451 to permitcoolant cascading over the windings 207 to exit the stator assembly 200into a drain port 503 of the baseplate 500 for external chilling andrecirculation.

The bearing housing 450 can generally be formed as a single piece suchas, for example, a machined forging, precision casting, machinedcasting, or combinations thereof). The bearing housing can beconstructed from any suitable material, such as, for example, cast A 536Grade 80-55-06.

Baseplate

The baseplate 500 provides a stable base for the flywheel 100, includingfastener holes for attachment of the flywheel 100 to a concretefoundation, as well as being wide enough and heavy enough to helpcounteract extreme loads in the event of a rotor release. For example,in some embodiments the baseplate 500 can have a diameter of about 60″and be about 8″ thick.

Furthermore, the baseplate 500 can provide a housing and attachment sitefor flywheel services and wires. For example, as shown in FIGS. 12A,12B, 12C, and 13 the baseplate 500 includes coolant supply ports 501 anddrain ports 503, vacuum ports 505. In addition, as shown in FIG. 13,wire connections 507 are provided for the stator windings as well as forany shaft position encoders 413 or other sensors. The baseplate 500 alsoserves as the resting plate and neutral anchor point for the rotor shaft401, bearing housing 450, and flywheel housing 600.

Flywheel Housing and Lid

Referring now to FIG. 13, the flywheel housing 600 and Lid 650 areconfigured to act as a containment vessel and, in combination with thebaseplate 500, to provide necessary sealing for the flywheel system tooperate in a vacuum. In some embodiments, the housing 600/lid 650structure can be configured to be much heavier than a loose rotor andthe lid 650 in particular can be configured to resist the extremevertical load of a loose rotor. To that end, in some embodiments, theflywheel housing 600 can be, for example, 0.5″ thick and made of 304stainless steel or similarly high strength material. The lid 650 canalso made of 0.5″ 304 stainless steel. In some embodiments, the housing600 can be secured to the baseplate 500 with 30 one inch bolts andsimilarly, to the lid 650 with an additional 30 one inch bolts.

Containment Liner

Referring now to FIG. 14, a containment liner 700 can be positionedaround the rotor 300 inside the housing 600. In some embodiments, thecontainment liner can be positioned such that it is free to spin betweenthe rotor 300 and the housing 600. In general, the containment linerabsorbs the angular momentum of a burst or overspeed flywheel rotor 300.Because the containment liner 700 is free to spin between the housing600 and the rotor 300, the containment liner 700 will rotate on contactin the event of a rotor burst and, as such, will absorb some, or evenall, of the rotor's 300 angular momentum energy in the event of a burst.In order to withstand or at least partially absorb such an event, thecontainment liner can generally be about 0.5″ thick and constructed from4130 steel or a similarly strong, ductile material.

External Components

Referring now to FIG. 15, in some embodiments, external components suchas a separate power electronics/motor control cabinet 900 can be used tocontrol operation of the flywheel 100. Additionally, in someembodiments, an external vacuum pump system 801 can be used to maintaina pumped vacuum within the flywheel 100. Furthermore, a cooling systempump and heat exchanger 803 can be provided for cooling andrecirculation of coolant flowing through the flywheel 100.

In general, the vacuum pump system 801 keeps the chamber in which theflywheel operates at vacuum conditions of well less than 1 torr. In someembodiments, the vacuum pump system can include, for example, a 7CFM,two-stage, rotary vane vacuum pump and accompanying active vacuum switchand transmitter. However, it will be apparent in view of this disclosurethat any vacuum pump system 801 suitable for maintaining a desiredvacuum in a particular size and configuration of flywheel 100 can beused in accordance with various embodiments.

In order to dissipate heat generated by the flywheel 100, the coolantpump/heat exchanger 803 can include, for example, a 65,000 BTU/hr fancooled heat sink, a 45-gallon reservoir, and a coolant filter (e.g., a25-micron filter), and a 14-20 gallon per minute coolant pump. However,it will be apparent in view of this disclosure that any coolantpump/heat exchanger 803 suitable for cooling a particular size andconfiguration of flywheel 100 can be used in accordance with variousembodiments.

Power Electronic/Motor Controller

Referring now to FIG. 16, an exemplary motor controller/power electronicunit 900 is shown. In general, the motor controller/power electronicunit 900 provides a connection between the live 3^(rd) rail and theflywheel. It, effectively, tells the flywheel when to store energy andspin the wheel in “motor mode” and when to discharge energy back to thesystem and operate in “generator mode”. This is the “motor controller”function.

The motor controller/power electronic unit 900 also provides theregulation capability to allow the 3^(rd) rail to accept the energy fromthe regenerative braking system. In particular, the motorcontroller/power electronic unit 900 regulates the amount of currentdelivered from the flywheel to the third rail to avoid overloading thethird rail during discharge.

Rapid Rail Transit Embodiment

As shown in FIG. 15, a flywheel 100 as described herein can be used inconnection with a rapid rail transit system 800. Rail cars todaydissipate large amounts of energy when braking. However, rapid transitsystems have not been able to utilize regenerative braking because thereis no power management system to be able to absorb and store the energyfrom the 3^(rd) rail and then deploy the energy back into the 3^(rd)rail. Due to energy savings, peak power reduction and lower T&D costs,this is an untapped market nearly $10B in size. By diverting the energyfrom the 3^(rd) rail into one or more flywheels 100 as described herein,such energy can be stored and then released back into the rail systemto, for example, deliver power for accelerating the rail car upondeparture from the station. Thus, the flywheel systems described hereinprovide safe operation of a power management system to be able tocapture the savings associated with regenerative braking.

As shown in FIG. 15 and described above, the flywheel 100 itself isoperated in conjunction with external components such as a separatepower electronics/motor control cabinet 900 can be used to controloperation of the flywheel 100. Additionally, in some embodiments, anexternal vacuum pump system 801 can be used to maintain a pumped vacuumwithin the flywheel 100. Furthermore, a cooling system pump and heatexchanger 803 can be provided for cooling and recirculation of coolantflowing through the flywheel 100.

In a rapid transit context, the motor controller/power electronic unit900 provides the connection between the live 3^(rd) rail and theflywheel. It, effectively, tells the flywheel when to store energy andspin the wheel in “motor mode” and when to discharge energy back to thesystem and operate in “generator mode”. That is, the motorcontroller/power electronic unit 900 provides the regulation capabilityto allow the 3^(rd) rail to accept the energy from the regenerativebraking system.

In particular, without a gating mechanism and a “sink” such as theflywheel assembly 100, introducing all of the regenerative brakingenergy to the third rail during braking would over-load the third rail.This phenomenon, in conventional rapid transit systems, causes most ofthe energy produced by a regenerative braking system to be dissipated(wasted) in resistor banks on the roof of the train. By using the motorcontroller/power electronic unit 900 to shunt the regenerative brakingenergy from the 3^(rd) rail to the flywheel assembly 100 (the “sink”), ahigh percentage of the regenerative braking energy can be diverted tothe flywheel assembly 100 for storage and subsequent, more gradualdischarge when needed, without overloading the third rail. Thereby, theenergy produced by the regenerative braking can be captured and used,rather than dissipated and wasted. In practice, the regenerative brakingpower (electrical current) comes into the 3^(rd) rail by design of thebraking system.

While the foregoing description of the invention enables one of ordinaryskill to make and use what is considered presently to be the best modethereof, those of ordinary skill will understand and appreciate theexistence of variations, combinations, and equivalents of the specificembodiments and examples herein. The above-described embodiments of thepresent invention are intended to be examples only. Alterations,modifications and variations may be effected to the particularembodiments by those of skill in the art without departing from thescope of the invention, which is defined solely by the claims appendedhereto. The invention is therefore not limited by the above describedembodiments and examples.

Having described the invention, and a preferred embodiment thereof, whatis claimed as new and secured by letters patent is:

What is claimed is:
 1. A composite rotor comprising: a rotor bodyextending along a longitudinal axis, the rotor body including: a firstcomponent extending longitudinally along at least a portion of the rotorbody, and a second component extending longitudinally along at least aportion of the rotor body, at least a portion of the second componentdisposed concentrically around the first component; wherein the firstcomponent and the second component together define an internal region,wherein a radial thickness of the first component and a radial thicknessof the second component vary along the longitudinal axis; and at leastone magnet disposed on an inner surface of at least one of the firstcomponent or the second component within the internal region.
 2. Thecomposite rotor of claim 1, wherein: the first component is constructedof a first fiber-reinforced composite; and the second component isconstructed of a second fiber-reinforced composite.
 3. The compositerotor of claim 2, wherein the first fiber-reinforced composite of thefirst component is overwound with the second fiber-reinforced compositeof the second component to form the composite rotor.
 4. The compositerotor of claim 2, wherein the first and second fiber-reinforcedcomposites are each constructed from at least one of a glass fiber, anaramid fiber, a carbon fiber, a quartz fiber, a boron fiber, a ceramicfiber, a natural fiber, or combinations thereof.
 5. The composite rotorof claim 4, wherein a resin matrix of each of the first and secondfiber-reinforced composites is constructed from at least one of apolyester resin, a vinylester resin, an epoxy resin, a phenolic, acyanate ester, a silicone, a polyurethane, a bismaleimide, a polyimide,or combinations thereof.
 6. The composite rotor of claim 2, wherein thefirst fiber-reinforced composite includes a glass reinforcing fiber. 7.The composite rotor of claim 2, wherein the second fiber-reinforcedcomposite includes a carbon reinforcing fiber.
 8. The composite rotor ofclaim 2, wherein a same resin matrix is used in both of the first andsecond fiber-reinforced composites.
 9. The composite rotor of claim 2,wherein a resin matrix of the first fiber-reinforced composite isdifferent than a resin matrix of the second fiber-reinforced composite.10. The composite rotor of claim 1, wherein: the second componentfurther comprises an internal recess, and the first component isdisposed in the internal recess.
 11. The composite rotor of claim 10,wherein the inner surface on which the at least one magnet is disposedis an inner surface of the second component, the inner surface beinglongitudinally spaced apart from the internal recess of the secondcomponent in which the first component is disposed.
 12. The compositerotor of claim 1, wherein an inner bearing surface of the firstcomponent is operatively engaged with a rotor hub.
 13. The compositerotor of claim 1, wherein the rotor body and at least one magnet form acomposite rotor of a flywheel energy storage system.
 14. The compositerotor of claim 1, wherein the rotor body includes a third componentextending longitudinally along a portion of the rotor bodylongitudinally spaced apart from the first component, at least a secondportion of the second component disposed concentrically around the thirdcomponent, wherein a radial thickness of the third component variesalong the longitudinal axis.
 15. The composite rotor of claim 1, whereinthe third component is constructed of at least one of the firstfiber-reinforced composite or a third fiber-reinforced composite.